Passengers with the condition, which can be deadly, can try to ensure a peanut-free flight. But even the best plans sometimes don't work.

Passengers with the condition, which can be deadly, can try to ensure a peanut-free flight. But even the best plans sometimes don't work.

Recently, while returning from vacation on a flight from London to Boston, I sat helplessly in a passenger seat while the flight attendants dealt with an emergency. This particular crisis had nothing to do with mechanical failure, weather or air rage. The problem was linked to peanuts.

Just before flight attendants had completed the main-cabin beverage and peanut service, a frightened woman leapt from her seat. "You're not supposed to serve peanuts on this flight!" she screamed. "I'm allergic to peanuts!"

Startled attendants stared in disbelief, wondering if the passenger had gone mad.

As it turned out, the woman was lucid and, more important, correct.

While making reservations for the flight, the woman told the airline she suffered from a severe peanut allergy and thus would be carrying a prescribed medication (Epipen adrenaline) that could be self-administered if exposed to peanuts.

These two conditions, set forth by the Air Carrier Access Act (the federal law governing transportation of passengers with disabilities), needed to be met in order for the airline to accept her medical certificate for travel.

Having met the requirements, the woman boarded our trans-Atlantic flight. She knew the Department of Transportation requires airlines to create a "peanut-free buffer zone" (at least three rows for passengers who document severe allergy to peanuts).

But she also knew that many carriers, including this one, provide an extra measure of protection. Because she had declared her allergy, peanuts would not be handed out on the flight, even though the caterer mistakenly placed the little bags onboard.

Thus, this passenger became hysterical when bags of salted peanuts appeared within a few feet of her.

Along with shellfish allergy, peanut allergy is one of the most dangerous. But in most cases, shellfish has to be ingested to cause a reaction. Peanut allergy is unusual in that a person can suffer severe health complications simply by breathing the air from an open bag of peanuts. This is particularly worrisome on airplanes because ventilation systems recirculate cabin air.

An estimated 3-million Americans suffer from this allergy. The symptoms, which can include severe swelling of the throat and mouth, vomiting and loss of consciousness, are referred to as anaphylactic shock. In severe cases it can be deadly.

Last year, 4-year-old Rachel Benway boarded a flight with her mom. According to the Bangor Daily News, Sherry Benway spoke to the unnamed airline on six occasions before the flight to make sure the carrier was aware of her daughter's severe peanut allergy. The airline assured her that peanuts would not be served on the flight. And peanuts were not served.

But the aircraft had not been properly cleaned, Benway said later, and "Peanut particles were everywhere." To make matters worse, passengers were given granola bars that contained peanut oil. Rachel's condition is apparently so severe, she reacts to even the aroma of peanut oil.

While unsuspecting passengers munched on the granola bars, Rachel began to have difficulty breathing. Benway administered antihistamine and epinephrine to counteract the symptoms. Rachel survived, but on the return flight, her mom made adjustments. She passed out her own snacks to nearby passengers, replacing the granola bars in the process.

Affected passengers need to know that most airlines cannot guarantee a peanut-free flight. For instance, other passengers cannot be prevented from bringing peanut-based food aboard. Airlines are required only to create a peanut-free buffer zone, which, as mentioned earlier, is not a sure-fire defense against airborne peanut proteins.

But the buffer zone had not been created on my flight. Despite the passenger's meticulous preflight measures, she found herself surrounded by bags of salted peanuts. Perhaps the reservations agent failed to input the proper warning in the passenger's computer record. Maybe the warning had been filed but the gate agent failed to inform a flight attendant. Perhaps the agent did inform a flight attendant but because of a nasty preflight incident, peanut allergies had been forgotten. (After launching a verbal assault on other passengers, the cabin crew and the gate agents, a woman was forcibly removed from the aircraft on orders from the captain for refusing to move an improperly stowed carry-on.)

Still, none of these reasons can excuse the blunder. No less than 100 bags of peanuts had been distributed when the allergic passenger leapt from her seat.

Luckily, the purser -- the chief flight attendant -- came to the rescue. A quick-thinking woman whose two children suffer from a rare yeast allergy (she told me this later), the purser suspended the peanut service and rushed the woman to a seat in the forward section of business class, far away peanuts, peanut oil fumes and airborne peanut proteins.

But what do our premium-class passengers munch on before dinner? As is the case with many airlines, they feast on almonds. Not peanuts.

- For the past 16 years, Elliott Hester has flown for a major U.S. carrier. His book, Plane Insanity: A Flight Attendant's Tales of Sex, Rage, and Queasiness at 30,000 Feet, will be published by St. Martin's Press in November. E-mail him at uzapme@msn.com.